Embodiments disclosed herein relate to exhaust systems and more particularly to the reduction of exhaust gas temperature from a diesel particulate filtering system.
Elevated exhaust gas temperatures from the tail pipes of diesel engine equipped motor vehicles have become a greater problem with the introduction of diesel particulate trap/filters (DPF) and the need to regenerate these filters. Diesel particulate filters remove unburned and partially burned hydrocarbons from the exhaust streams produced by diesel engines. A DPF may be periodically regenerated by raising the temperature in the filter sufficiently to accelerate the oxidation of or ignite the particulate matter trapped in the filter. This process, once initiated, further increases the temperature of the exhaust stream downstream from the filter. The increase in the temperature of the exhaust may singe passers-by, particularly where the exhaust is discharged near ground level, and add stress on exhaust pipes.
Some prior systems achieved exhaust gas cooling as a byproduct of cooling a component, such as a muffler, in the exhaust system. In some contemporary pollution control schemes, components of the exhaust gas treatment system must run hot in order to operate or regenerate, making it undesirable to reduce exhaust gas temperature ahead of the component in question or to reduce the temperature of the component itself. For example, diesel particulate filter regeneration requires maintaining the temperature of the filter during regeneration.
A conventional method of cooling exhaust gases is an “in-can” or “in-muffler” venturi device. In the path of exhaust gas flow, the venturi device is located downstream of the muffler and upstream of the tailpipe, and uses ambient air to lower the overall temperature of the gases emitted from the tailpipe. In the venturi device, a “cold pipe” draws in ambient air, and sits within a “hot pipe” that forms the path of flow of the exhaust gases. The exhaust gases travel within the hot pipe and around the cold pipe. As the exhaust gases travel around the cold pipe, the exhaust gases are cooled. At an outlet of the cold pipe, the ambient gases and the exhaust gases are mixed in the tailpipe for further cooling. However, new emissions laws require that the exhaust gas temperatures be lowered beyond the capabilities of the conventional in-muffler venturi device.
Reducing the exhaust gas temperature after leaving the diesel particulate filter can be accomplished with a temperature control device. The temperature control device typically has inlets that allow fresh air into the device to mix the exhaust gas with the air to reduce the temperature of the exhaust.